Aspects of the present invention relate to an aligned discontinuous fiber composite and method of manufacture for production of highly aligned discontinuous fiber composite material that is comprised of a highly aligned discontinuous fiber dry preform, that can be impregnated with a polymer and consolidated or cured to produce prepreg, multi-layer blanks or a composite structure with high fiber volume fraction. Aligned discontinuous fiber composite materials, sourced as new, chopped from continuous or recycled fiber reinforcement, can offer stiffness and strength comparable to continuous fiber composites, provided similar fiber volume fractions can be achieved (˜55-60% for high-performance composite materials). In addition, they offer benefits of lower cost and provide significant processing advantages in terms of drapability, formability and steerability.
Aligned discontinuous fiber composites enable high levels of in-plane deformation (extension and shear), interlayer slip and compressibility when deformed as a dry preform prior to impregnation with polymer, or within a composite blank material during forming of all types (vacuum forming, bladder forming, sheet forming, stamp forming, etc.). Blanks can be multi-layer with any stacking sequence. Layer thickness is controlled during the alignment process and combined with the preforming methods, enable preforms and prepregs with controlled areal weight (thin-ply 8 grams/m2 (or lower) to standard 190 grams/m2 or higher) and composite blank manufacture for minimum gage applications. Fabrication of complex geometry composite structures with aligned discontinuous fiber forms eliminate complex ply patterns and darting, improves quality (eliminates wrinkling common to continuous fiber) and reduces preform costs. These attributes makes this composite material suitable for complex geometry production of aerospace parts, automotive products, consumer electronic products, sporting goods and any lightweight product that requires laminate forms with high curvatures and tight radius features, properties equivalent to continuous fiber and lower part cost. This composite material is ideal for replacement of metal parts produced by sheet forming and stamping at high rates.
Additionally, the ability to use discontinuous fibers from recycled composite materials creates a low-cost material source allowing near 100% property translation of recycled materials for reuse in parts of equal value (downcycling to make parts of lower value can be minimized).
Aligned discontinuous fiber composite materials can also be used as a source material for FDM (Fused Deposition Modeling), 3D additive processing and in tape form for automated fiber or tape placement processing of large structures. These processes can leverage the anisotropic performance of continuous fiber composite properties using aligned discontinuous fibers within that structure that requires complex coursing and non-geodesic paths, to meet design requirements for optimized structural performance. In tow and tape form, aligned discontinuous fiber processing by FDM and advanced tape placement can be steered to greater angles without wrinkling. Current approaches to fiber-reinforced feedstock for additive manufacturing have limitations in achievable fiber volume fractions (less than 25% compared to 55-60% for high-performance), which limits part performance. Aligned discontinuous fiber feedstock with volume fractions approaching 60% would represent a significant improvement in performance for additively manufactured parts. Discontinuous fiber architecture will allow complex geometry manufacture enabled by in-plane stretch and steerability. Thin ply formats (15-125 μm in single ply thickness) allow for very fine tailoring of stacking sequence during FDM.
Hybridized aligned discontinuous fibers offer multifunctional properties at lower cost while maintaining manufacturing advantages. Hybridization can occur at the fiber level within a single layer as well as traditional hybridization on a layer to layer basis or both. Multifunctional properties include mechanical (stiffness, strength, fracture toughness and ductility), thermal, electrical, and electromagnetic properties, etc. This process controls fiber and matrix type, fiber length and aspect ratio, fiber volume fraction and layer thickness. This process allows for combining and highly aligning any number of fiber types (structural or non-structural) and their weight fractions into a highly aligned discontinuous layer. It also offers the ability to manufacture co-mingled preforms by mixing and aligning of polymer fibers at the filament level that form the matrix with any combination of structural and non-structural fibers.
One challenge encountered when fabricating a highly aligned discontinuous fiber ply is developing a process or combination of processes that can align large quantities of individual discontinuous fibers to a high degree at high volume fractions and low cost to be competitive with current continuous fiber ply production, while having comparable or superior mechanical properties. Historically, discontinuous fiber composites are produced without controlled alignment as a randomly oriented system (random mat), a discontinuous fiber chopped prepreg in a thermoplastic or thermoset matrix, or within an injection or compression molded composite where fiber orientation is governed by fluid (resin) flow behavior within a cavity. These historical processes result in low stiffness and strength when compared to continuous composite structures.
A comprehensive review of prior art in highly aligned discontinuous fiber composites is available in the literature. See, e.g., Such, M., Ward, C., & Potter, K. (2014). Aligned discontinuous fibre composites: a short history. Journal of Multifunctional Composites, 2(3). Highly aligned discontinuous fiber composites have been fabricated with two general approaches, with alignment methods for discontinuous fibers of a specific length, or by inducing fiber breaks in continuous fiber bundles or tows. As has been documented in the literature, the latter approach creates a heterogeneous microstructure with non-uniform fiber lengths with lengths generally an order of magnitude larger (greater than 50 mm for 5-7 micron carbon fibers) than makes rapid forming of complex geometries difficult.
WO 2014/170637 A1, (HiPerDiF process) describes a manufacturing process for aligning discontinuous fibers in a water suspension flowing in a channel comprised of a pair of solid surfaces or walls to create tape with fibers aligned in the belt direction. The technique shows good alignment, but only discloses production of aligned fibers along the belt travel direction and is limited in throughput and width production. Composite performance with this approach has shown 75% or less strength translation compared to a continuous fiber equivalent, as well as fiber aspect ratios less than 500. The physics of fiber alignment is different with respect to the process described herein capable of producing sheets of any width. Additionally, the process disclosed in WO 2014/170637 discloses only the formation of relatively small-width tapes with all fibers aligned with the length of the tape.